[R] Date Not Staying in Date Format

[David Randel]

I have a column in a data frame that has a class of "Date" and a mode of 
"numeric".  When I:

max(df$Date)

My output stays in Date format, i.e. "2006-01-03".

However, when I run the following statment:

tapply(df$Date, df$SomeFactor, max)

my output looks like this:  9129   9493   9861  10226  10591  10956  11320  
11687  12052  12417

The returned object is of mode "numeric" and class "array".  Each array 
element is of mode "numeric" and class "numeric".  I believe that this is 
the integer representation of my date.  I can't seem to convert it back to a 
date.

How do I get these to be intrepreted as a date instead of a number?

Thanks,
~Dave R.